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Mariana Babayeva MD, PhD Touro College of Pharmacy, New York, NY, USA Page 1 Compound extracted from plant Aristolochia Nephrotoxin and carcinogen Page 2 AA-I is an organic anion eliminated by the kidney Produces nephrotoxic effect to S3 segment of renal proximal tubule Chinese herbs nephropathy (CHN) Page 3 Herbal remedies Belgian nephropathy Slimming pills: Balkan endemic nephropathy (BEN) Bread contaminated by Aristolochia fangchi Aristolochia clematitis Glomerular Filtration • GFR: glomerular filtration rate Tubular Secretion • Active transport • Secretion transporters: OATs, OCTs, etc. Tubular Reabsorption • Active transport • • Reabsorptive transporters Passive transport Page 4 Glomerular Filtration (1) Tubular Secretion (2) Tubular Reabsorption (3) Renal Excretion (4) • OAT system plays an important role in tubular secretion and reabsorption of compounds (organic anions) Human: Rodent: OAT1 OAT2 Oats1 Oat2 Oat3 Oat4 Oat5 OAT3 OAT4 Page 5 The overall goal of the research was to assess transport mechanism of renal excretion of AA-I. Further identify potential strategies to mitigate drug toxicity by reducing renal uptake Page 6 Step 1 Step 2 Step 3 HPLC Method Protein Binding Studies IPK Stuides Assessment of renal drug excretion mechanism - Dose-linearity - Inhibition studies Drug interaction screening Model for nephrotoxicity Probing renal drug metabolism Gender differences in renal function and drug excretion Correlation between drug excretion and membrane transporter expression Model for aging Studies in mutant strains (genetic “knockout” animals) cannulate for kidney perfusion cannulate for urine collection Krebs-Henseleit buffer (KHS buffer) Bovine serum albumin (BSA) Dextran Glucose Inulin Amino acids ◦ Mixture of 20 amino acids Treatment Group Control Perfusion Compound(s) (Concentration) Justification None Establish viability of preparation and allow for evaluating of drug effects on kidney function AA-I Excretion Aristolochic acid I (20uM) AA-I Transport Inhibition Aristolochic acid I (20uM) + Probenecid (1mM) Obtain baseline parameter values of renal excretion and of AA-I Study mechanisms of AA-I renal transport Viability Parameters GFR Minimum Acceptable Value > 0.5 ml/min Glucose Reabsorption (FRGlu) > 90% Sodium Reabsorption (FRNa) > 85% Urine Flow Rate > 0.03 ml/min dXU Clr XR dt Cp Clr fu GFR • dXU/dt = urinary drug excretion rate • Cp = perfusate drug concentration • • • • XR = excretion ratio CLr = clearance fu = fraction unbound GFR = glomerular filtration rate XR > 1 = net secretion process XR < 1 = net reabsorption process Protein Binding of AA-I IPK Viability Parameters AA-I Renal Excretion Parameters Ultrafiltration technique was used for the protein binding studies Table 1. Summary of AAI Protein Binding Studies in Perfusate There were no significant differences in protein binding among the different concentrations of AA-I (ANOVA, p >0.05) Table 2. Effect of Probenecid on AAI Protein Binding in Perfusate There was no significant difference in protein binding between the two study groups (ANOVA, p >0.05) Kidney function was well maintained across all study groups The IPK technique has been successfully applied Table 5. Summary of AAI Renal Excretion Parameters in IPK The renal excretion parameters ~ 2-fold higher in studies with PBC Effect of Probenecid on AA-I Excretion in the IPK. Plot of Cumulative Amount of AA-I Excreted in Urine vs Time. XR of AA-I < 1 (0.08 and 0.17) for both study groups The results suggest net reabsorption XR of AA-I was more than 2-fold higher in the presence of probenecid Probenecid inhibited the tubular reabsorption of AA-I most probably by interaction with renal organic anion transport system The amount of unrecovered AA-I in Phase I studies was 3-fold higher than in Phase II Probenecid decreased accumulation of AA-I in the kidney cells Page 22 Bidirectional Transport: Oat2 / Oat5 Page 23 • The S3 segment of proximal tubule is the most vulnerable part to AA-I toxicity • Rat Oat2 and Oat5 are localized to the apical membrane of S3 segment of proximal tubules • Oat2 and Oat5may take part in active renal reabsorption of AA-I • Reabsorption of AA-I by Oat2 and Oat5 may cause tubular injury of S3 segments of proximal tubules • AA-I has a high affinity to Oat2 • Inhibition of reabsorption can decrease nephrotoxicity of AA I Previous findings Assumption Page 24 The present study described the transport mechanism of Aristolochic acid I renal excretion The observation suggested that the renal apical transporters (Oat2 and Oat5) may function as reabsorptive pathway during renal elimination of AA-I. Inhibition of AA-I reabsorption can decrease nephrotoxicity of AA-I. This assumption requires further investigation Page 25